References considered to be relevant as background to the presently disclosed subject matter are listed below:    [1] U.S. Pat. No. 4,118,137    [2] U.S. Pat. No. 4,166,049    [3] U.S. Pat. No. 4,180,730    [4] U.S. Pat. No. 4,021,393    [5] U.S. Pat. No. 4,069,182    [6] U.S. Pat. No. 6,346,561    [7] PCT Patent Publication No. WO 2012/131605    [8] US Patent Application No. 2010/0056669    [9] US Patent Application No. 2011/0233105    [10] U.S. Pat. No. 8,182,726    [11] PCT Patent Publication No. WO 2013/132488    [12] US Patent Application No. 2013/0116364    [13] US Patent No. 2015/0080505
Acknowledgement of the above references herein is not to be inferred as meaning that these are in any way relevant to the patentability of the presently disclosed subject matter.